We compiled the available observations of surface O3
at Mt. Tai – the highest mountain in the North China Plain, and found a significant increase of O3
concenrations from 2003 to 2015. The observed O3
increase was mainly due to the increase of O3
precursors, especially VOCs. Our analysis shows that controlling NOx
alone, in the absence of VOC controls, is not sufficient to reduce regional O3
levels in North China in a short period.